Bonaparte's initial invasion of Egypt in 1798 and his subsequent attack upon Turkish held Syria in the following year meant that a large part of his Army of the Orient as taken up with garrisoning the conquered lands and in sieges such as that of Acre.
The need for more men to continue the campaign was paramount but was further aggravated by the effective blockade of Egypt by the British since their victory at the battle of the Nile and Aboukir bay (1798). Many of the surviving French sailors from Aboukir were formed into Legion Nautique which was raised in French held Alexandria in the autumn of 1799. The infantry wore the distinctive round naval hat while the officers wore tailcoats and bicornes. They were initially used as headquarters staff, along with e recently raised Guides a pied, but the acute shortage of manpower meant that the Legion Nautique was subsequently distributed amongst the demi-brigades, artillery and the engineers of the Army of the Orient, and fought with it through to the battle of Alexandria and the final withdrawal from Cairo in 1801.